To date, the availability of mammalian oocytes has been a limiting factor in studying their molecular and chemical properties. A technique has now been developed (Dunbar and Hedrick) to isolate 40,000 porcine oocytes in 6-8 man hours. Zona pellucida ghosts can be easily obtained from these samples. Using this technique it is proposed to (1) determine the physicochemical nature of the macromolecules of the porcine zona pellucida; (2) characterize the molecule(s) responsible for the immunological cross-reactivity between pig and human zona pellucida and investigate possible cross-reactions with other mammalian systems, including non-human primates; and (3) determine the origin of the porcine zona pellucida. It is anticipated that physicochemical studies will provide a basis for formulating molecular studies on sperm-zona and egg-zona interactions at fertilization.